| Black carbon (BC), which is one of the widespread organic matters in soils and sediments, possesses high adsorptivity towards hydrophobic organic compounds (HOCs), thus it determines the migration and transformation of HOCs to some extent in the environment. However, when BC is released into the environment, its surface and adsorption properties will change because of its interaction with the dissolved organic matters (DOMs) and mineral substance. As one of the main sources of BC in the environment, rice-straw-derived biochar (RBC) was used as research object and pentachlorophenol (PCP) was used as representative pollutant in this dissertation. In order to discover the influence of DOMs on the adsorption properties of RBC, the influence of aging process on the adsorption and desorption of PCP by the S+RBC, S+RBC+DOMs (mixed system) and S+DOMs/RBC (preloaded system) treatments were compared. The study will provide a theoretical foundation for the application of RBC in the remediation of soils or sediments contaminated with HOCs. The main conclusions are as follows:(1) RBC possesses high pore structure, large BET surface area and abundant surface functional groups, such as carboxyl and lactone groups. After loading with humic acid or alanine, the BET surface area of RBC decreased, the average pore size and the number of surface acidic functional groups increased, and humic acid showed more significant effect than alanine in the process.(2) The adsorption isotherms of PCP by RBC were nonlinear and could be well simulated by Freundlich and Dual-mode models. The adsorption capacity of RBC was suppressed more significantly by humic acid than alanine. When RBC was loaded with humic acid or alanine, the adsorption simulated parameters Kf, Qmax.L/(KD KL.D) decreased, n, KD increased, and the adsorbability decreased faster with the increase of pH, which indicated that the adsorption of PCP by RBC was mainly through surface adsorption, hole filling and interaction between surface functional groups.(3) The addition of humic acid, alanine, or RBC to sediment could improve the adsorption of PCP, but the adsorbability was even less than the sediment supplemented with RBC alone when they were added at the same time. With the increase of aging time, the adsorbability of all the treatments decreased. It was found that the adsorbability of S+RBC+DOMs treatment showed the fastest descent rate, meanwhile, S+DOMs/RBC treatment showed the slowest descent rate with time increasing, and adsorption curves of S+RBC and S+RBC+DOMs became closer to S+DOM/RBC gradually. Therefore, it can be concluded that DOMs played the key role in the descent of RBC adsorbability in aged sediments. The adsorption contribution of RBC to the whole sediment treatments was still greater than70%and RBC still played the key role in the migration and transformation of PCP in sediments after aging for60d.(4) The Tenax-mediated desorption of PCP from sediments exhibited triphasic kinetics (i.e. fast, slow and very slow desorption fractions); the addition of RBC could decrease the desorption amount and average desorption rate and increase the very slow desorption fraction. With the increase of aging time, the rapid, slow desorption fractions of PCP increased and the very slow desorption fraction decreased, and correspondingly the average desorption rate constants increased. The desorption parameters in S+HA/RBC treatment showed the least significant variation in the comparison of S+RBC, S+RBC+HA and S+HA/RBC treatments, while S+RBC+HA treatment showed the most significant variation. As for S+RBC+HA treatment, the presence of humic acid made the descent of RBC adsorptivity faster, thus, the very slow desorption fraction decreased, the average desorption rate and the desorption amount of PCP increased.(5) In the RBC added system, the adsorption parameters had a good linear correlation with the Tenax-mediated desorption amount and very slow desorption fraction, thus the adsorption datas could be used for the estimation of release situation of PCP from the contaminated sediments. In addition,12h Tenax desorption amount was the most suitable interval for the representative of fast desorption amount. |
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